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Hi ,
im new to the forum . I have a question what is the bestethod to bore a briggs engine? I have been working on small engines for over 15 years but have never learned to bore a cylinder and i am curious and would like to learn more about it . I have a briggs motor ive honed replaced the rings ect and put it all back together and it has low compression 40 lbs. I will have to bore it to use bigger rings right ? What is the best way to bore a small engine Thanks
John

John, 40 pounds is Low... are you sure you are not having valve problems?
Was there any ridge that may have cracked the new top ring... I would look closer at things before I packed it off to a shop with the proper tooling... What B&S engine is it? :smile:KennyV

Personally I would not try to bore the engine myself unless I have a boring machine. I agree with Kenny that you should check the valves and rings first.

Yes I agree, I also would check the valves first.

I'm no expert, but I think if you bore the cylinder you will need to replace pistion to the proper size. If you are able to get away with just honing then you can probably get away with a little larger set of rings. Before this happens you really need to inspect the cylinder for imperfections an maybe so some measurement with a snap gauge and micrometer.

I disagree with honing and just new rings. If oil is getting past the rings 90% of the time the cylinder is either worn more than .003 (which is usually the smallest larger ring) or out of round. The only time I recommend honing is when you are doing a rebuild due to internal engine failure (crank, govenor, rod, etc) where you want to install rings in an engine with low hours. Honing and new rings will only solve a oil or compression problem 10% of the time at the most. As long as you have the head off and are checking the valves, take the six measurements of the cylinder as you would for cylinder analysis and see how they match with cylinder specs. This will tell you how to proceed.

Well to give some history on the engine it broke the connecting rod and i decicec to open it up to see how bad the damage was . After checking it out the scoring on tue cylinder wasnt bad i honed it and put in another connecting rod piston and new rings .... i did it mostly to see if i could save the motor but standard size rings arent enough to hold compression now i guess

Did you take any measurements before you installed the new rings. If you did would you post them and the engine numbers. Maybe you can still save it, depending on the measurement, with out a Hugh expense.

The tedious method of bore measurement is with a telescoping guage at numerous points. As you may know they are read with a micrometer and easily misread due to not being square in bore. The best is to take it to a motorcycle shop and have someone check the bore with a dial bore guage. This will be accurate and clearly show taper and out-of- round . I am not familiar with small engine repair parts, but many times there are standard overbore piston diameters such as .010" and .020" over. Although there is such a thing as "power " honing for small overbores, a true boring machine is usually called for if enough cylinder wall is present to accept the overbore. Honing is then done to create a proper finish on the cylinder wall for oil retention during break in.

If the cylinder walls are so bad on a Briggs engine that it needs to be rebored you will need this done at a machine shop. Then you will have to buy oversize pistons and rings. This is if you can find them. If I were you I would check on the price of a new short block or a good used engine. We have our pulling tractors rebored all the time but this is for more power and we also buy custom made pistons and rods to change our stroke, sorry now I am getting into something all together different.

jetrail said:

Hi ,
im new to the forum . I have a question what is the bestethod to bore a briggs engine? I have been working on small engines for over 15 years but have never learned to bore a cylinder and i am curious and would like to learn more about it . I have a briggs motor ive honed replaced the rings ect and put it all back together and it has low compression 40 lbs. I will have to bore it to use bigger rings right ? What is the best way to bore a small engine Thanks
John

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Has this engine ever ran since you did this hone job and re-assembled.? If it has, I have another question.

If you haven't been successful in getting it started since that work was done I have a suggestion.

This thread seems dead, but I couldn' resist answering. Your solution is to perform a leakdown test. With both valves closed (motor at TDC on compression stroke), air should not be able to leak out of the engine, except a small percentage past the ever-present ring leakage.

Not only will performing a leakdown test tell you the percentage of cylinder leakage you have, but the escaping air pressure will also point out where it's leaking out at. Inevitably, it's almost always out one of the two valves (due to valve or valve adjustment issues), past the rings (due to ring sealing or bore issues), past the head gasket (due to bad gasket or warped block or head), or out the piston (thru a hole in the top or side).

With a leakdown test, you can't miss.

FYI, because of the fairly low cost of small engines to be replaced with a new or used one, spending big bucks on properly machining a new bore is rarely worth it unless you do it yourself. And even if you're not great at it, as long as you have a dial bore gauge to use, you can do it good enough to make plenty of compression to get a lawn mower engine to run adequately. It's not a V8 race engine here.

I got the motor broken . Never got it running and i. Took a shot at it just for the experience . Once my customer repairs die down i might tinker with it again . It had a brokend connecting rod when i got it ect

The leak down test is an excellent way to get down to the nitty gritty and tell exactly where the leak is.

Often a quicker way to tell if the rings only is where the leak is, squirt about a teaspoon of oil in the spark plug hole and repeat the compression test. If the rings are the culprit the oil will usually temporarily seal the rings and increase compression. If there is a leaking valve or other opening the added oil usually doesn't increase compression.

With only 40 lbs. compression one can usually hold his thumb on the plug hole. With compression in the good enough to start range - 70 -- 80 - it's difficult. That's just another quick way to tell if your endeavors have accomplished anything.

A good way to check for cyl wear is to get a new set of rings, set one of the compression rings squarely half way down in the cyl (using the piston) Then using a feeler gauge, measure the ring gap. I don't know what engine you have, but ring gap reject specs are readily available.

On another note and a cool tip is when your con rod gave out. If this was due to lack of oil and some of the aluminum from the con rod was transfered to the crank pin, DO NOT USE ABRASIVE! Get yourself an empty quart oil container and cut the top off leaving about 2 inches from the bottom. Then cut a "V" in each end. Set your crank in the "V" cut outs in a mannor that the crank pin is in the down position. From your swim pool supplies, get some muratic acid and fill that container so the acid covers the crank pin. This acid will eat the aluminum off the crank but will not attack the steel crank pin. (I hope this was clear)

Thanks for the tips everyone. I know my way pretty well around a small engine but the tips you guys are giving me ive never used . Plus with repairs dying down in the next two months or so i like to tinker with equipment that is mine and i have replaced connecting rods and crankshafts but never brought one back that was like this so i have always wanted to learn how to bore a cylinder just for the experience ect .